1. Field of the Invention
The present invention relates to a fuel cell system including a fuel cell stack formed by stacking a plurality of power generation cells, and a reactant gas supply mechanism having an ejector for supplying a reactant gas to a fuel cell stack, and returning the reactant gas discharged from the fuel cell stack after consumption to the fuel cell stack.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs an electrolyte membrane (electrolyte) comprising a polymer ion exchange membrane. The electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (electrolyte electrode assembly). The membrane electrode assembly is sandwiched between separators to form a power generation cell. In use, normally, a predetermined number of power generation cells are stacked together to form a fuel cell stack.
In the fuel cell, a fuel gas such as a hydrogen gas is supplied to the anode, and a fuel off gas containing the fuel gas which has not been consumed in the power generation reaction is discharged from the fuel cell. Therefore, in the fuel cell, in the interest of economy, in order to effectively use the fuel gas, in general, the fuel off gas is supplied again to the anode as the fuel gas.
For example, as shown in FIG. 15, a fuel cell system disclosed in Japanese Laid-Open Patent Publication No. 2004-095528 includes a hydrogen supply channel 3 for supplying hydrogen from a hydrogen supply apparatus 1 to a fuel cell 2 (a stack body formed by stacking a plurality of power generation cells 2a), an off gas circulation channel 4 for merging the off gas discharged from the fuel cell 2 into the hydrogen supply channel 3 and supplying the off gas to the fuel cell 2 for recycling the off gas in the fuel cell 2, an ejector pump 5 circulating the off gas to the off gas circulation channel 4, while being capable of controlling the circulation amount of the off gas and mixing the off gas to the hydrogen in the main supply, and a pressure sensor 6 for detecting the pressure of the off gas ejected from the ejector pump 5.
In the case where the ejector pump 5 is provided in the vicinity of the fuel cell 2, since the high pressure hydrogen is ejected from the ejector pump 5 into the hydrogen supply passage of the fuel cell 2, static pressure distribution tends to occur in the hydrogen supply passage. Thus, in the fuel cell 2, in particular, the hydrogen is not sufficiently supplied to the power generation cell 2a provided at the hydrogen inlet, and the power generation performance is lowered undesirably.